Breathing apparatus

ABSTRACT

A face mask ( 10 ) mechanically coupled to a lung demand valve (LDV) ( 12 ). The face mask ( 10 ) comprises a main mask and an inner mask ( 15 ) which fits over the wearer&#39;s mouth and nose. The interior of the inner mask ( 15 ) is in fluidic communication with the interior of the main mask ( 10 ) by means of non-return valves ( 16 ). The interior of the main mask is in fluidic communication with an inlet port ( 18 ) which is mechanically and fluidically coupled to a supply port ( 20 ) of an LDV. The LDV ( 12 ) includes a diaphragm and a cover ( 44 ) which comprises three parts ( 44   a,    44   b ) and ( 44   c ). Exhaled air is used to flush the space around the diaphragm. Thus, any toxic or undesirable gas in the vicinity of the diaphragm is pushed out to atmosphere by the exhaled air flowing past and around the diaphragm.

FIELD OF THE INVENTION

The present invention relates to self-contained breathing apparatus(SCBA) and particularly to breathing apparatus utilising a face mask anda second stage regulator, or so-called lung-demand-valve (LDV).

In a SCBA set breathing gas (usually air) is stored at a first, “high”pressure in a pressurized cylinder. From the cylinder the gas isconveyed to the user for breathing via at least one stage of regulator,in which the gas is reduced in pressure. It is preferable to have twostages of regulator each of which reduces the pressure. In such a systemthe first reduction in pressure takes place, as the gas leaves thecylinder, in a first stage regulator. The gas is stored in the cylinderat a pressure of typically up to 200 to 300 bar and after the firststage of pressure reduction has a pressure in the order of 7.5 bar. Thegas is then considered to be at “medium” pressure. The medium pressuregas is then conveyed to a second stage regulator, usually a lung demandvalve conveniently mounted on a face mask of a user. Here the gas isreduced in pressure to a slightly super-atmospheric pressure, at whichthe gas is breathable.

The lung demand valve is actuated by the breathing of the wearer of themask, such that as the wearer inhales a diaphragm is displaced causing avalving member to open allowing breathable gas into an expansionchamber, from which it may be drawn into the lungs of the user.

An example of such apparatus is illustrated in schematic sectional viewin FIG. 1, in which a face mask 10 is mechanically coupled to a lungdemand valve 12, which in turn is in fluidic communication with acylinder of breathing gas 13 via a hose 14. The face mask 10 comprisesan inner mask 15 which fits over the wearer's mouth and nose. Theinterior of the inner mask 15 is in fluidic communication with theinterior of the main mask 10 by means of so-called “oranasal” non-returnvalves 16, mounted on either side of the inner mask, and the interior ofthe main mask is in fluidic communication via vents (not shown) with aninlet port 18 of the mask. The mask inlet port 18 is mechanicallyfluidically coupled to a supply port 20 of the LDV. The LDV 12 itselfincludes a valving member, a valve seat (neither shown) and an expansionchamber 22. The valving member is biased in the “valve closed” positionin which it bears against the valve seat. However, the valving membermay be displaced from the valve seat to allow medium pressure compressedair into the chamber 22 by movement of an actuator arm 24 mountedpivotally on the LDV. The compressed air arrives at the LDV from arubber hose coupled to the LDV at medium pressure (approximately 7.5bar). A distal end 24A of the arm bears against the diaphragm member 26comprising a flexible apron portion 26A and, in the centre, a relativelyrigid disc portion 26B. The apron portion 26A is mounted around itsperiphery in a correspondingly shaped housing portion 28 of the LDV.Beneath it is a spring 30 which exerts a biasing force on the diaphragmto keep the actuator arm 24 normally in such a configuration that thevalve is slightly open. On the same side of the diaphragm as the spring30 the housing portion 28 is open to atmosphere, through a rubber dustcover 32 which is clipped over the housing 28 to keep dust or otherambient particulates from contacting the diaphragm 26.

In equilibrium, the spring 30 positions the diaphragm 26 and hence theactuator arm 24 so that the valve is partially open. Accordingly,breathable gas, at slightly super atmospheric pressure, flows into thechamber and hence to the mask inlet port 18 at a constant, limited rate,and the pressure inside the LDV keeps the spring and diaphragm in anequilibrium position. As soon as the wearer of the mask inhales, areduction in the pressure inside the mask 15 occurs. This reduction istransmitted to the LDV chamber 22. The diaphragm is in fluidiccommunication with the atmosphere through holes 34 in the base of theLDV housing. When the air pressure in the chamber 22 falls below theequilibrium, super-atmospheric pressure, the spring 30 is able to pushthe diaphragm, causing it to rise, which in turn causes the actuator arm24 to rise until they adopt the position shown in FIG. 1. The result ofthis is that the compressed air flows into the chamber 22 at a greaterrate during inhalation. Once inhalation has ceased the pressure inchamber 22 builds again to resume the equilibrium state of slightlysuper-atmospheric pressing down on the diaphragm and countering theforce of the spring 30. This causes the actuator arm to urge the valvetowards an equilibrium position in which the flow of breathable gas intothe chamber 22 is reduced again.

In this way the valve acts to supply breathable air to the lungs of thewearer but “on demand”, whilst keeping a constant low level of supply tomaintain a positive (i.e. super atmospheric) pressure in the mask at alltimes, even during non-inhalation phases, so as to resist the ingress ofsmoke and noxious gases into the mask around its sides.

FIG. 2 shows schematically the exhalation phase. In the LDV the pressurein chamber 22, i.e. of air for inhalation, and spring 30 maintains thediaphragm 26 and actuator arm 24 in an equilibrium position shown inFIG. 2. Meanwhile, exhaled air in the inner mask 15 builds in pressureand at a one-way exhalation valve 36 overcomes a biasing spring 38 toallow an exhale valving member 40 to be displaced from its seat 42. Theexhaled air is simply vented to atmosphere to outlets 39. Onceexhalation ceases, the pressure of exhaled air in the face mask fallsand biasing spring 38 closes the exhalation valve 36. The cycle ofinhalation and exhalation then continues.

For the LDV to function, the diaphragm must be exposed to the externalatmosphere on one side. In atmospheres containing relatively highconcentrations of toxins it is conceivable that the external face of thediaphragm might be subjected to a gradual build up of toxins. Since theapron of the diaphragm is a thin membrane, typically of rubber orsilicone, concerns have been expressed that in exceptional cases if thediaphragm faces this exposure repeatedly or for long periods this couldlead to toxins diffusing through the membrane.

SUMMARY OF THE INVENTION

Accordingly, a need exists for an LDV and/or LDV/mask combination inwhich the likelihood of such a build up of toxins on the external faceof the diaphragm is minimised or eliminated.

According to one aspect of the invention there is provided a lung demandvalve device for use with breathing apparatus, for delivering breathablegas from a pressurised supply to a user wearing a face mask, forinhalation. The device comprises a body in which is housed a valvemember, for controlling the rate of delivery of the breathable gas, amovable diaphragm having a first face exposed to pressure within thebody and a second face exposed to pressure outside the body. Thediaphragm is responsive to the differential in pressure between itsfirst and second faces to control the valve member. A duct is providedand arranged to direct exhaled air towards the second face of thediaphragm.

The device may be detachably mountable on a mask of a breathingapparatus. Alternatively the device may be permanently attached to amask of a breathing apparatus. In an alternative arrangement the deviceis integral with a mask of a breathing apparatus.

The duct portion may be arranged to abut an exhalation port of a mask.The duct may be arranged to direct exhaled air to a region surroundingthe second face of the diaphragm, so as to flush ambient gases from thatregion.

Preferably the device comprises a cover member arranged to extend aroundthe device for preventing the ingress of dirt into the housing, andwherein the duct comprises a portion of the cover. The cover maycomprise a plurality of portions which portions are detachably fixedtogether.

Preferably the device comprises locating means arranged to co-operatewith a mask to inhibit rotation of the device relative to a mask.

According to another aspect of the present invention there is provided alung demand valve suitable for use in a self contained breathingapparatus, in which fluid for breathing is conveyed to a user oninhalation. The lung demand valve comprises a first fluid path, a secondfluid path, a flexible diaphragm, separating the first and second fluidpaths, and wherein the second fluid path is open to the atmosphere.

According to a still further aspect of the present invention there isprovided a cover suitable for use on a lung demand valve for a selfcontained breathing apparatus, in which fluid for breathing is conveyedto a user on inhalation. The lung demand valve comprises a first fluidpath, and a diaphragm, enclosing at least a part of the first fluidpath. The cover provides the lung demand valve with a second fluid path,so that the first and second fluid paths are separated by the diaphragm,and the second fluid path is open to the atmosphere, and wherein exhaledfluid is directed along the second fluid path to the diaphragm.

According to a still further aspect of the present invention there isprovided a self-contained breathing apparatus in which fluid forbreathing is conveyed to a user on inhalation. The apparatus comprises aface mask, connected to a lung demand valve, and worn by the user, ahigh pressure cylinder containing the fluid for breathing, a hose forconveying fluid from the cylinder to the lung demand valve. The lungdemand valve comprises a first fluid path for conveying fluid forinhalation to the face mask, a second fluid path for conveying exhaledfluid from the face mask to the atmosphere; and a flexible diaphragm,separating the first and second fluid paths, wherein exhaled air isdirected to the diaphragm.

Preferably the second fluid path is provided by a removable coverpositioned over the lung demand valve.

The cover may be made of chemically resistant material.

BRIEF DESCRIPTION OF THE DRAWINGS

A preferred embodiment of the present invention will now be described,by way of example only, with reference to the accompanying drawings inwhich:

FIG. 1 is a schematic sectional view of a prior known breathing mask andLDV in a first configuration,

FIG. 2 is a view of the mask of FIG. 1 in a second configuration,

FIG. 3 is a side view of mask and LDV according to one exemplaryembodiment of the invention,

FIG. 4 is a front prospective view of the LDV of FIG. 3, and

FIG. 5 is a schematic sectional view of the mask and LDV of FIGS. 3 and4.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Turning to FIG. 3, this is a side view of a mask and LDV constructed inaccordance with one exemplary preferred embodiment of the presentinvention. In particular, FIG. 3 shows a mask 10, an LDV, generallyrepresented by 12, a cylinder 13 and hose 14, and an inner mask 15complete with non-return valve 16. The mask 10, LDV 12 cylinder 13 andhose 14 are identical to the equivalents shown in FIGS. 1 and 2 and,during an inhalation phase, they operate in the same manner as the priorart apparatus described above.

However, in accordance with the present invention the LDV 12 is providedwith a cover 44 which comprises three parts, namely, a yoke, 44 a, arubber cover portion 44 b and a rigid plastic duct portion 44 c.

The rigid plastic yoke 44 a extends across the top of the supply port(not shown) of the LDV and is secured by screws 46 (only one of which isshown in FIG. 3). The screws are located on both sides of the yoke andthreadedly engage the rigid plastic duct portion 44 c. Stretched betweenthe yoke 44 a and the rigid plastic duct portion 44 c across the frontand underside of the LDV is the rubber cover portion 44 b. Inparticular, the flexible rubber cover portion 44 b is trapped betweenthe yoke 44 a and duct 44 c at its upper end, and engages lugs (notshown) on the duct 44 c at its lower end. A gap in the cover portion 44b reveals a compressed air intake port 48 which in the interest ofclarity is shown in this figure unconnected to any delivery hose.

FIG. 4 shows generally the LDV 12 in a front perspective view. In FIG.4, only parts 56, 58, and 60 of the face mask 10 to which the LDV iscoupled are shown by hatched lines in the interest of clarity. A portion50 of pressurised rubber hose is also shown connected to the intake port48 of the LDV cover through which “medium” pressure air is supplied tothe LDV.

FIG. 5 shows a cross-sectional view of the mask. As the wearer exhales,an increased pressure is created in the inner mask 14. The increasedpressure in the face mask lowers the diaphragm 26 in the LDV,temporarily closing the air supply. As the user breathes out, theexhalation valve 36 opens and allows the exhaled air to pass out of themask 10 through outlet port 39. Since the duct portion 44 c of the cover44 abuts directly the port 39, exhaled air is retained within anddirected by the cover 44. The air then flows over the diaphragm 26, andis eventually vented to the atmosphere through exit slots 52. When theuser ceases exhaling, the exhalation valve 36 is urged shut by thespring 38, thus closing the exhalation port 39 to the atmosphere. Theuser then breathes in, and the process described above in relation toFIG. 1 is repeated.

Accordingly, exhaled air which in the prior art apparatus would bevented directly to the atmosphere is used to flush the space around thediaphragm. Thus, any toxic or undesirable gas in the vicinity of thediaphragm is pushed out to atmosphere by the exhaled air flowing pastand around the diaphragm.

In the prior art LDV and mask the LDV is free to rotate in relation tothe mask whilst remaining coupled thereto. Clearly in the apparatusaccording to the present invention the LDV must not be permitted torotate with respect to the mask, since such rotation would displace theduct 44 c from the exhalation port 39 and thus the exhaled air wouldundesirably vent directly to atmosphere before flushing the diaphragm26.

To maintain the abutment of the duct 44 c to the exhalation port 39, theyoke portion 44 a of the cover is provided with two upstanding lugs 54(see FIG. 4) which lie either side of a pair of similar lugs 56 on theface mask which are provided as standard items to protect a releasebutton 58, located on the mask from being inadvertently depressed.

The juxtaposition of lugs 54 and 56 respectively on the yoke portion ofthe LDV cover and on the face mask, prevents rotation of the LDV, andhence the duct 44 c, with respect to the mask.

While the invention has been described in detail and with reference tospecific examples thereof, it will be apparent to one skilled in the artthat various changes and modifications can be made therein withoutdeparting from the spirit and scope thereof.

1. A lung demand valve device for use with breathing apparatus, fordelivering breathable gas from a pressurised supply to a user wearing aface mask, for inhalation, the device comprising a body in which ishoused a valve member, for controlling the rate of delivery of thebreathable gas, a movable diaphragm having a first face exposed topressure within the body and a second face exposed to pressure outsidethe body, the diaphragm being responsive to the differential in pressurebetween its first and second faces to control the valve member, and aduct arranged to direct exhaled air towards said second face of saiddiaphragm.
 2. A device according to claim 1 wherein the device isdetachably mountable on a mask of a breathing apparatus.
 3. A deviceaccording to claim 1 wherein the device is permanently attached to amask of a breathing apparatus.
 4. A device according to claim 1 whereinthe device is integral with a mask of a breathing apparatus.
 5. A deviceaccording to claim 1 wherein the duct portion is arranged to abut anexhalation port of a mask.
 6. A device according to claim 1 wherein theduct is arranged to direct exhaled air to a region surrounding thesecond face of the diaphragm, so as to flush ambient gases from saidregion.
 7. A device according to claim 1 wherein the device comprises acover member arranged to extend around the device for preventing theingress of dirt into the housing, and wherein the duct comprises aportion of said cover.
 8. A device according to claim 7 wherein saidcover comprises a plurality of portions which portions are detachablyfixed together.
 9. A device according to claim 1 wherein the devicecomprises locating means arranged to co-operate with a mask to inhibitrotation of the device relative to a mask.
 10. Self-contained breathingapparatus including a lung demand valve device according to claim
 1. 11.A lung demand valve suitable for use in a self contained breathingapparatus, in which fluid for breathing is conveyed to a user oninhalation, the lung demand valve comprising: a first fluid path, asecond fluid path, a flexible diaphragm, separating the first and secondfluid paths, and wherein the second fluid path is open to theatmosphere.
 12. A cover suitable for use on a lung demand valve for aself contained breathing apparatus, in which fluid for breathing isconveyed to a user on inhalation, in which the lung demand valvecomprises: a first fluid path, and a diaphragm, enclosing at least apart of the first fluid path, wherein the cover provides the lung demandvalve with a second fluid path, so that the first and second fluid pathsare separated by the diaphragm, and the second fluid path is open to theatmosphere, and wherein exhaled fluid is directed along the second fluidpath to the diaphragm.
 13. A self-contained breathing apparatus in whichfluid for breathing is conveyed to a user on inhalation, the apparatuscomprising: a face mask, connected to a lung demand valve, and worn bythe user, a high pressure cylinder containing the fluid for breathing, ahose for conveying fluid from the cylinder to the lung demand valve,wherein the lung demand valve comprises: a first fluid path forconveying fluid for inhalation to the face mask, a second fluid path forconveying exhaled fluid from the face mask to the atmosphere, and aflexible diaphragm, separating the first and second fluid paths, whereinexhaled air is directed to the diaphragm.